This present invention relates in general to protection of infrared sensing device, and more particularly, to a monolithically integrated uncooled infrared sensing device using IC foundry compatible processes.
Uncooled infrared detectors have recently gained wide attention for infrared imaging applications, due to their advantages such as low cost, low weight, low power, large spectral response, and long-term operation compared to those of photon detectors. Worldwide effort is still continuing to implement very large format arrays at low cost for use in various applications, including commercial applications such as driver's night vision enhancement and fire fighting. One of the main issues for achieving low-cost detectors is their monolithic integration and compatibility with CMOS technology.
The most widely used uncooled detector approach is to implement microbolometers using surface micromachined bridges on CMOS processed wafers, where infrared radiation increases the temperature of a material formed on the thermally isolated and suspended bridge, causing a change in its resistance related to its temperature coefficient of resistance (TCR). Vanadium oxide, which is the most widely known and used microbolometer material, has a high TCR of about 2-3%/K; however, Vanadium oxide is not a standard material in IC fabrication and requires dedicated expensive equipment to prevent contamination of the CMOS line. In addition, it exhibits large noise due to its monocrystalline structure. There are efforts to implement surface micromachined microbolometers using IC compatible materials such as amorphous silicon, amorphous silicon carbide, and polycrystalline silicon-germanium; and these materials also have high TCR values of 2.5%/K, 4-6%/K, and 2-3%/K, respectively. However, these materials require high temperature annealing to reduce their residual stress, which is not suitable for post-CMOS processing for monolithic integration. In addition, they exhibit even higher noise than Vanadium oxide due to their monocrystalline structures.
Thus, it is desirable to improve incumbent infrared sensing devices.